yThe objective of our research was to study the movements the mosquito Aedes albopictus. This mosquito transmits more than 20 viruses to humans throughout the world and is the vector of the recent major epidemics of Dengue and Chikungunya on Reunion Island and the Indian Ocean Region and is, therefore, of great interest for human health. We set out to determine whether reservoirs of populations could be found in natural environments and whether or not these populations are capable of re-colonising urban areas. Until now, only limited data has been available on the population dynamics of Aedes albopictus in this part of the world, information critical for guiding vector control strategies and predicting or preventing epidemics. We chose two areas where a serious CHIKV epidemic occurred. We then used genetic markers and ecological data to estimate patterns of gene flow and behaviour. We were able to demonstrate that populations were structured with limited gene flow despite observing migration. We found that Ae. albopictus preferred urban areas for mating and to lay their eggs because of the availability of hosts and permanent containers that favoured higher mosquito densities. We also show, however, that natural environments are reservoirs for re-colonisation of urban areas.